Circuit arrangement for the frequency modulation of a carrier wave



Feb. 13, 1951 G. HEPP 2,541,649

CIRCUIT ARRANGEMENT FOR THE FREQUENCY MODULATION OF A CARRIER WAVE Filed April 27, 1946 GERARD HEPR 11v VEN TOR.

17 18 \yfi I y AGJEWT.

Patented Feb. 13, 1951 UNITED STATES GIRGUILII ARRANGEMENT FORv THE FRE- QUENCY; MODULATION OF A CARRIER WAVE.

Gerard-Hepp, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank. WIIdaTDuSji: (Eompany, Hartford, Conn,v as

trustee.

ApplibationAprilZ'i, 1946, Serial No. 665 389 In the-Netherlands June 30, 1-942 S&o,tion 1-,,Bublic:LaW 690, August 8, 1946 Ratenhexpires June 30, 1962 For modulating the frequency of carrier waves generated bya high-frequency oscillator it is known to use a so-called, reactance tube whose mutual conductance is governed by. the, modulating oscillation. It is naturally desirable that the frequency deviations. should vary linearly with the; modulation voltages. and, if a reactance. tube is used in the known manner, this will generally only be thefcase within. a, limited zone of the control range of the tube and,. if operating and bias voltages are carefully chosen,.to a satisfactoryapproximation. If ,When. in use, the. tube is subjected to variations, in. the course off time, as is always the-case, the quality of; the. modulation is more and more affected so, that. readjustment is repeatedly necessary.

According to the invention,, these disadvantages are obviated by. the use of. anode modulation instead of mutual conductancer modulation inthe reactance tube.v

In order that the invention may, be. clearly understood and readily carried inefiectitlwill now bedescribed more.fullywithreference to the. accompanying drawing, forming apart. of the specs ification and in.which Fig. 1- is a schematic diagramofia modulation circuit arrangement. according, to. the. invention,

Fig. 2 is a schematic diagram; of. another em.- bodiment of the modulation circuit. arrangement according to the invention, ,and

Fig. 3 is a. further embodimentof a. modulation circuit arrangement. according to. the. invention.

Referring to Fig.1, the anode. circuit. of'aselfoscillatingoscillator valve l includesa. tuned circuit 2, 3 which determines the. mean. frequency. A small condenser 5 couplestheanode.circuit. of valve l to the control grid. of areactance. valve 6. The resistance 1 connects the. said control grid to-the cathode of. the valve 6. Due to. the fact that the impedanceof. the condenser. 5" is large compared with the resistance. 1, the; grid voltage of the valve 6. will. lead the anodevoltage of the oscillator valve I by about,90.,.as will also be the case with thecurrentsupplied from the reactance valve. This current passesthrough two series-connected coils. 8. and. 9'. and. through the secondary coil of a transformer H1. on, the primary coil of which the modulation voltages are; impressed. The coil 8. iscoupled. to a. coil H included in theanode circuit of, thevalve I and the coil 9; is coupled to the coil. 2. of the tuning; circuit- 2,, 3, the. couplingsdoeing so. chosen that voltagefrom-the; oscillator: valve I; practically does not reach the anode circuit of the 2 modulation valve 6 and the anode circuit. of the oscillator valve 1 is not directly influenced by the modulating voltage. In operation, the anode current of the reactance valve 6' which leads. the anode voltage of the valve lby is modulated in amplitude by the modulating voltage. which is impressed on the anode circuit of'the valve 6 via transformer l0. These modulated, currents are induced in' the tuning circuit 2, 3 ,,by the coil 9. Tuning circuit 2, 3ialso has theunmodfulate'd anode current of the oscillator valve. lpassing through it. This results in a variation inthe frequency determined by the. resonant. circuit 2, 3 which varies linearly with the. modulation vol'tages if the anode. current of the valve 6' is.mod-

ulated by these voltages in. a: sufiici'ently linear manner. For the very purpose of obtaining this effect it is desirable that care should be taken that novoltage from oscillator valve l. is directly impressed on the circuit of the reactance valve. 6.

A circuit arrangement. which offers. advantages in adjustability at higher frequenciesis shown in Fig. 2.

In this embodiment, the reactance valve 6 which, as before, is modulated. in its anode. circuit is not connected'directl'y in parallel withthe tuning circuit 2, 3, of' the generator valvel but a tube I2 is interposed betweenthe tube 6 and tube I. The grid of tube l2is connectedto. the anode of the tube. 6 by means of. a blocking. condenser l3. In this circuit arrangement. care should be taken that the. tube IZihas, a sufii'ciently linear characteristic curve or else. that the lat.- ter is straightened in known manner. by feedback coupling.

In the embodiment shown in Fig. 3, the. modulation is effected by meansof' a diode 5.4 which acts as a limiter and whose threshold. value is determinednotonly by a. battery IliT-bnt also. by the modulation voltageto be appliedbetween. the terminalsv iii-l6. The. external. circuit of. the tube. includes a. circuit. I i. which is. tuned to. the mean frequency anddampedbya parallel'resistance l8. The oscillations-displaced. in phase by 90 are supplied. to. the diode. system through. a resistance l9. and the modulated.phase-displaced oscillations are applied, similarly to Fig..2',.t'o. the controligridoia buffer. valve l2.

Thethreecircuit arrangements shownare. all simplex. It... is, however, possible. without fur. ther precautions to use push-pullconnected tubes in, all. three cases, with similar attendantwellknown advantages.

What .I claim-is;

1. A circuit arrangement for frequency modulating a carrier wave, comprising a carrier frequency oscillator circuit having a first electron discharge tube having an anode, a control grid and a cathode, a resonant circuit coupled to the anode of said first discharge tube to determine the central frequency of the oscillations produced by said oscillator circuit, a reactance tube circuit comprising a second electron discharge tube having an anode, a control grid and a cathode, means to couple said resonant circuit to the control grid of said second tube to apply a phase quadrature voltage thereto, means to apply operating potentials to said tubes, means to amplitude-modulate the anode potential of said reactance tube to produce amplitude-modulated oscillations substantially 90 out of phase with re spect to the carrier frequency oscillations of said oscillator circuit, means to couple the output of said reactance tube circuit to said resonant circuit to combine the carrier frequency oscillations and the amplitude-modulated quadrature oscillations to produce a frequency-modulated carrier Wave, and to couple the anode circuit of said first tube in opposition to the output circuit of said second tube effectively to isolate the anode of said first tube from the modulating potential applied to said reactance tube circuit.

2. A circuit arrangement for frequency modulating a carrier Wave, comprising a carrier fre quency oscillator circuit having a first electron discharge tube having an anode, a control grid and a cathode, a resonant circuit coupled to the anode of said first discharge tube to determine the central frequency of the oscillations produced by said oscillator circuit, a reactance tube circuit comprising a second electron discharge tube having an anode, a control grid and a cathode, a capacitor coupling said resonant circuit to the control grid of said second tube to appiy a phase quadrature voltage thereto, means to apply operting potentials to said tube, means to amplitude-modulate the anode potential of said reactance tube to produce amplitude-modulated oscillations substantially 90 out of phase with respect to the carrier frequency oscillations of said oscillator circuit, means inductively coupling the output of said reactance tube circuit to said resonant circuit to combine the carrier frequency oscillations and the amplitude-modulated quadrature oscillations to produce a frequencymodulated carrier wave, and a transformer having the primary Winding thereof connected in series with said inductive coupling means and the sec-- ondary connected in series with said resonant circuit to couple the anode circuit of said first tube in opposition to the output circuit of said second tube effectively to isolate the anode of said first tube from the modulating potential applied to said reactance tube circuit.

3. A circuit arrangement for frequency modulating a carrier wave, comprising a carrier frequency oscillator circuit having a first electron discharge tube having an anode, a, control grid and a cathode, a resonant circuit coupled to the anode of said first discharge tube to determine the central frequency of the oscillations produced by said oscillator circuit, a reactance tube circuit comprising a second electron discharge tube having an anode, a control grid and a cathode, means to couple said resonant circuit to the control grid of said second tube to apply a phase quadrature voltage thereto, a third electron discharge tube having an input circuit and an output circuit, means to apply operating potentials to said tubes, means to amplitude-modulate the anode potential of said second tube to produce amplitude-modulated oscillations substantially 90 out of phase with respect to the oscillations of said oscillator circuit, means to couple the anode of said second tube to the input circuit of said third tube, and means to couple the output circuit of said third tube to said resonant circuit to combine the carrier frequency oscillations and the modulated quadrature oscillations to produce a frequency modulated carrier Wave.

4. A circuit arrangement for frequency modulating a carrier Wave, comprising a carrier frequency oscillator circuit having a first electron discharge tube having an anode, a control grid and a cathode, a resonant circuit coupled to the anode of said first discharge tube to determine the central frequency of the oscillations produced by said oscillator circuit, a reactance tube circuit comprising a second electron discharge tube having an anode, a control grid and a cathode, a capacitor coupling said resonant circuit to the control grid of said second tube to apply a phase quadrature voltage thereto, a third electron discharge tube having an input circuit and an output circuit, means to apply operating potentials to said tubes, means to amplitude-modulate the anode potential of said second tube to produce amplitude-modulated oscillations substantially out of phase With respect to the oscillations of said oscillator circuit, a second capacitor coupling the anode of said second tube to the input circuit of said third tube, and means to couple the output circuit of said third tube directly to said resonant circuit to combine the carrier frequency oscillations and the modulated quadrature oscillations to produce a frequency modulated carrier Wave.

5. A circuit arrangement for frequency modulating a carrier Wave, comprising a carrier frequency oscillator circuit having a first electron discharge tube having an anode, a control grid and a cathode, a first resonant circuit coupled to the anode of said first discharge tube to determine the central frequency of the oscillations produced by said oscillator circuit, a second electron discharge tube having an anode and a cathode, means coupling said resonant circuit to the anode of said second tube to apply a phase quadrature voltage thereto, a third electron discharge tube having an anode, a control grid and a cathode, a second resonant circuit tuned to said central frequency and coupled to the control grid of said third discharge tube, means to damp said second resonant circuit, means to apply operating potentials to said tubes, means to apply modulating potentials to said second discharge tube to produce amplitude-modulated oscillations in quadrature with the oscillations of said oscillator circuit, means to bias said second tube to limit the applied modulation potential to values above a predetermined value, means to couple the anode of said second tube to the control grid of said third tube, and means to couple the anode of said third tube to said first resonant circuit to combine the carrier frequency oscillations and said amplitude-modulated quadrature oscillations to produce a frequency-modulated carrier wave.

6. A circuit arrangement for frequency-modulating a carrier wave, comprising a carrier frequency oscillator circuit having a first electron discharge tube having an anode, a control grid and a cathode, a first resonant circuit coupled to the anode of said first discharge tube to determine the central frequency of the oscillations produced by said oscillator circuit, a second electron discharge tube having an anode and a cathode, a first capacitor coupling said resonant circuit to the anode of said second tube to apply a phase quadrature voltage thereto, a third electron discharge tube having an anode, a control grid and a cathode, a second resonant circuit tuned to said central frequency and coupled to the control grid of said third discharge tube, a resistor shunting said second resonant circuit, means to apply operating potentials to said tubes, means to apply modulating potentials to the cathode of said second discharge tube to produce amplitude-modulated oscillations in quadrature with the oscillations of said oscillator circuit at the anode of said second tube, means to bias said second tube to limit the applied modulation potential to values above a predetermined value, means to connect the anode of said second tube directly to the control grid of said third tube, and means to connect the anode of said third tube directly to said first resonant circuit to combine the carrier frequency oscillations and said amplitude-modulated quadrature oscillations to produce a frequency-modulated carrier wave.

'7. A circuit arrangement for frequency-modulating a carrier wave comprising means including an oscillator electron discharge tube having an modulation means to prevent direct amplitude modulation of said oscillator tube means, and

, means to combine said first and second oscillations to produce a frequency modulated carrier wave.

GERARD HEPP.

REFERENCES CITED The following references are of record in the T file of this patent:

UNITED STATES PATENTS Number Name Date 1,777,410 Jones Oct. 7, 1930 2,350,171 Lawrence May 30, 1944 2,351,368 Roberts June 13, 1944 

